Molecular fingerprinting confirms extensive cow-to-cow intra-herd transmission of a single Mycobacterium bovis strain

In this study we have characterized M. bovis isolates from a herd of cattle in Uvalde, Texas in which 52 of the 193 animals selected at random in 1994 from a herd of 331 were caudal fold skin-test positive. Thirty-two of 52 s kin-test positive cattle had gross lesions at slaughter, and isolations of M. bovis were made from 29 animals. The herd was comprised of Red Devon cat tle purchased between 1978 and 1980 (n = 26) and breeding bulls (n = 3) int roduced at later times, and all were tuberculosis test negative at the time of purchase. Other animals were natural additions (offspring) of these cat tle. One additional animal, a Holstein present on the ranch at the time of purchase in 1976, was retained to nurse orphaned and weak calves. Using sev eral molecular fingerprinting techniques we have verified a clonal relation ship among the M. bovis isolates consistent with infection originating with a single strain. The molecular fingerprint patterns demonstrate the stabil ity of the profiles despite persistence and spread of the organism within t he herd for two decades and confirms their use in epidemiological tracing. (C) 1999 Elsevier Science B.V. All rights reserved.